White iron phosphate



3,407,034 WHITE IRON PHOSPHATE Leonard M. Bennetch, Bethlehem, Pa., assignor to Chas. Pfizer & Co., Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed June 16, 1965, Ser. No. 464,572 6 Claims. (Cl. 23-105) ABSTRACT OF THE DISCLOSURE Preparation of white iron phosphate particularly suitable for inhibiting corrosion in primer paints.

This invention relates to a process for the preparation of white iron phosphate. More particularly, it relates to a preparation of a white iron phosphate which is suitable as an agent for inhibiting corrosion in primer paints.

The herein disclosed process for preparing white iron phosphate, FePO .2H O, comprises commingling in water phosphoric acid, a ferrous salt selected from the group consisting of ferrous sulfate, ferrous chloride and ferrous nitrate and an oxidizing agent selected from the class con sisting of the alkali metal chlorates, ammonium chlorate and hydrogen peroxide, each of said acid and said oxidizing agent being added in sufiicient amount to provide at least one equivalent per equivalent of said ferrous salt, heating for at least A hour at a temperature of from 50 C. to about 95 C., adjusting the pH to a value of about 2 to about 6, and recovering White, insoluble iron phosphate which precipitates.

Although white iron phosphate has been prepared by various other processes, it has been found that the method disclosed herein offers distinct advantages over those described in the prior art. For example, various processes relate to the preparation of iron phosphate having a variable composition, i.e., hydrate compositions of varying proportions. This is not the case here since the product obtained by the process of this invention provides an iron phosphate having the definite composition FePO .2H O commonly called strengite. Further, the process herein affords an iron phosphate which exhibits a desirable white color of 90 to 95% relative dry brightness against a magnesium carbonate whiteness standard and a soft tex ture. Still further, the product so obtained possesses a fine particle size in the range from about /2 to 4 microns.

Another advantageous feature of the process of the instant invention concerns the recovery or precipitation step. Until the basic material, for example, sodium hydroxide, is added which permits the pH value of the resulting system to attain a reading of from 2 to 6, the reaction mixture remains as a clear, homogeneous solution. Upon addition of said basic material, precipitation of white iron phosphate commences as the pH of the system attains a value of from 2 to about 6. This method of mixing and heating reactants insures complete oxidation of ferrous iron and thus prohibits precipitation of undesired ferrous compound prior to the addition of alkali. Consequently, with complete oxidation, homogeneity of reaction is obtained and the ultimate precipitate is uniformly of the desired higher valence state of 3. Although complete neutralization may be effected, it is undesirable to do so in view of the fact that the color of the final product is adversely affected.

Further advantages associated with the aforementioned process consist of shorter overall reaction times and the isolation of a product free from contamination nited States Patent The process of this invention can he represented by the following chemical equation:

Of course, it is possible and within the scope of this invention to utilize chemical equivalents for 3 of the 4 reagents indicated in aforementioned general equation, i.e. ferrous sulfate, sodium chlorate and sodium hydroxide. For example, it is possible and Within the scope of this invention to utilize ferrous chloride or ferrous nitrate in place of ferrous sulfate so long as the basic stoichiometry of the reaction is unchanged. Similarly, in addition to sodium chlorate, other oxidizing agents may be utilized. Particularly effective oxidizing agents are potassium, lithium and ammonium chlorate and hydrogen peroxide; how ever, other suitable oxidizing agents include sodium peroxide and chlorine gas.

With regard to the basic material utilized, it is found that a wide variety of alkaline substances are suitable. For instance, in addition to sodium hydroxide, sodium carbonate, potassium hydroxide and ammonium hydroxide are similarly effective. Of course, it is understood that as with the previously mentioned reagents, the basic stoichiometry of the reaction must be satisfied.

The above molecular stoichiometry can be converted to an equivalent basis if the ferrous salt is chosen arbitrarily as a constant having a value of one equivalent. On this basis, an equivalent amount of phosphoric acid is an equimolar amount; an equivalent amount of a chlorate oxiding agent is a molar amount and of a peroxide is a /2 molar amount; and an equivalent amount of basic material is a two molar amount.

Although it is necessary to use at least 1 equivalent of phosphoric acid per equivalent of ferrous salt, it is possible and even desirable to use an excess of said phosphoric acid. In this connection, it is possible to use up to 3 equivalents of acid per equivalent of said ferrous salt, i.e., a 2 equivalent excess, however, it is preferred to use from about 1.1 to about 1.7 equivalents per equivalent of ferrous salt to secure a product of whiter color.

The oxidation step consists of simultaneously adding at least an equivalent amount of oxidizing agent, and heating the resulting mixture for at least hour at a temperature of from about 50 C. to about 95 C. In this regard, even at the lower temperature limits, there will be no need to continue heating for more than a period of 2-3 hours. The time factor, as is obvious, will depend on the temperature and the mole ratios of reagents wherein, in general, the higher the temperature, the shorter the oxidation period. Similarly, molar excesses of any one reagent or several reagents will enhance the rate of reaction. Most particularly preferred are temperatures in the range of from C. to about C. With regard to the oxidizing agent, it is preferred to use at least an equivalent amount per equivalent of ferrous salt, however, an excess will not cause any adverse effects. Although it is possible to use as much as a 2 equivalent excess, it is most preferred to use only an excess of about .1 to .5 equivalent.

The recovery or precipitation step consists of adding to the heated, oxidized solution while stirring, an aqueous solution of a basic material such as sodium hydroxide or sodium carbonate in a sufficient amount to provide at least one equivalent per equivalent of ferrous salt and recovering the precipitated white iron phosphate which forms. It is possible to add a slight excess of base, however, no advantage results from so doing. Depending on the amount of base used, the pH of the mixture at the 3. point where precipitation of iron phosphate is virtually complete will vary from a value of about 2 to about 6.

The yield of white iron phosphate is almost quantitative. The collection process consists of filtering, washing and drying utilizing conventional methods. The white iron phosphate, FePO .2H O, which is isolated analyzes approximately 42% Fe O 39% P and the balance free and combined water.

Iron phosphate prepared by the process of this invention has been found to be an effective corrosion-inhibitor in primer paints. The method of evaluating iron phosphate for anti-corrosion properties is demonstrated by the following series of tests:

(A) Salt Fog Resistance Test (B) Water Immersion Resistance Test (C) Humidity Resistance Test Standard automotive alkyd and epoxy primer surfacers were selected as test mediums. Controls were pigmented with an iron oxide-barium sulfate combination, a known corrosion inhibitive pigment combination, whereas the test samples were pigmented with iron phosphate. Paints were prepared of 18-gauge bonderized steel with each paint applied by spray at uniform dry film thicknesses of .91.0 mil. The panels obtained in this manner were subjected to tests B and C above.

With regard to test A above, each panel was coated with the test primer surfacer and cured whereupon the lower half of each test panel was top-coated with a black automotive type enamel and cured. Test panels were then scored in the form of an X and subjected to the Salt Fog Resistance test. After exposure of 1000 hours duration, the test panels were removed and the lower half of each was stripped of paint laying bare the steel substrate which revealed the degree of protection the primer surfacers and the top coated primer surfacer afforded the steel substrate.

The results of the aforesaid tests indicated that iron phosphate as prepared by the process disclosed herein resisted corrosion in a manner superior to iron oxide. Further, the panels containing iron phosphate exhibited virtually no blistering.

In addition to its use as an anti-corrosion agent in primer paints, iron phosphate is prepared herein, may also find utility, due to its chemical purity, as a food grade additive in foods, vitamin preparations and in feeds. Further, due to its chemical composition, it may have utility as a plant nutrient ingredient or fertilizer stabilizer.

The following examples are provided by way of illustration and should not be interpreted as limiting the invention, many variations of which are possible without departing from the spirit or scope thereof.

Example I With stirring, FeSO (2280 g., M) in 12.5 1. of solution is added to a 16 1. volume of water, followed by the addition of 85% H PO (1715 ml., 25 M). To this mixture is added 500 ml. of an aqueous solution containing 275 g., 2.6 M of NaClO whereupon the resulting mixture is stirred and heated to 85 C. for /2 hour. Precipitation of the white iron phosphate product is accomplished by gradually adding 16 l. of basic solution containing NaOH (1275 g., 32 M). During the addition of base, stirring and heating are continued and when precipitation is complete, the product is filtered, Washed and dried to give virtually a quantitative yield of white iron phosphate, FPO42H20.

Example II The procedure of Example I is repeated wherein a stoichiometric equivalent amount of ferrous chloride is used in place of ferrous sulfate with comparable results.

Example III The procedure of Example I is repeated wherein a stoichiometric equivalent amount of ferrous nitrate is used in place of ferrous sulfate with comparable results.

4 Example IV The procedure of Example I is repeated wherein the following equivalents of phosphoric acid per equivalent of ferrous sulfate are used:

FeSO, (equivalents): H PO (equivalents) instead of the ratio utilized in Example I with comparable results.

Example V The procedure of Example I is repeated wherein the oxidation step is carried out using the following FeSO /NaClO equivalent ratios and reaction conditions:

Substantially quantitative yields of white iron phosphate are obtained in each instance.

Example VI The procedure of Example I is repeated wherein the following equivalent amounts of sodium hydroxideper equivalent of ferrous sulfate are used:

FeSO, (equivalents) NaOH (equivalents) instead of the approximate 1:1 ratio used in Example I with satisfactory results.

Example VII With stirring, 284 ml. of an aqueous ferrous sulfate solution containing 70.5 g. of FeSO is combined with 500 m1. of water, and then with 52 ml. of an 85.3% phosphoric acid solution. Subsequently, 8.35 g., of NaClO in 50 ml. of water is added and the entire mixture diluted to a 2500 ml. volume with water, stirred and heated to temperature of 70 C. for a period of one hour. While maintaining said temperature and stirring, 500 ml. of an aqueous solution containing 51.2 g. of Na CO is added. Upon complete precipitation, the product is filtered, washed and dried to give virtually a quantitative yield of white iron phosphate, FePO -2H 0.

Example VIII The procedure of Example VII is repeated wherein a stoichiometric equivalent amount of ammonium hydroxide is used in place of Na CO with comparable results.

Example IX The procedures of Examples I, II, III, IV, V, VI, VII and VIII are repeated wherein a stoichiometric equivalent amount of potassium chlorate is used in lieu of sodium chlorate and satisfactory results are obtained.

Example X The procedures of Examples I, II, III, IV, V, VII and VIII are repeated wherein a stoichiometric equivalent amount of lithium chlorate is used in lieu of sodium chlorate and substantially the same results are obtained.

Example XI The procedures of Examples I, II, III, IV, V, VI, VII, and VIII are repeated wherein a stoichiometric equivalent amount of ammonium chlorate is used in lieu of sodium chlorate and substantially the same results are obtained.

Example XII The procedures of Examples I, II, III, IV, V, VI, VII and VIII are repeated wherein a stoichiometric equivalent amount of hydrogen peroxide is used in place of sodium chlorate and satisfactory results are obtained.

Example XIII The corrosion resistance of iron phosphate obtained by any of the synthetic methods outlined in Examples I to XII was measured in automotive primer sur-facers and a comparison made to a standard corrosion inhibitive pigment combination consisting of iron oxide and barium sulfate. These measurement studies consisted of three studies:

(1) Salt Fog Resistance Study (2) Water Immersion Resistance Study (3) Humidity Resistance Study and the following results are tabulated hereinbelow:

Salt fog study Each panel, prepared of 18-gauge bonderized steel, was coated with the primer surfacer (either control or test pigmentation) and cured. The lower half of each panel was top coated with a black automotive type enamel and cured. The panels were then scored by making 2 diagonal marks in the form of an X and Subjected to salt fog conditions. Following exposure of 1000 hrs. duration, the panels were removed and the lower half of each panel was stripped of paint laying bare the steel substrate, revealing the degree of protection the primer surfacers and the top coated primer surfacer afforded the steel substrate.

The results of the Water Immersion Study and Humidity Study shown above further indicate the ability of white iron phosphate to inhibit corrosion.

What is claimed is:

1. A process for the preparation of white iron phosphate of the formula FePO -2H O which comprises commingling in water phosphoric acid, a ferrous salt selected from the group consisting of ferrous sulfate, ferrous chloride and ferrous nitrate and an oxidizing agent selected from the class consisting of the alkali metal chlorates, ammonium chlorate and hydrogen peroxide, each of said acid and said oxidizing agent being added in sufficient amount to provide at least one equivalent per equivalent of said ferrous salt, heating for at least hour at a temperature of from C. to about 95 C., adjusting the pH to a value of about 2 to about 6, and recovering white, insoluble iron phosphate which precipitates.

2. A process as in claim 1 wherein said ferrous salt is ferrous sulfate.

3. A process as in claim 1 wherein said oxidizing agent is sodium chlorate.

4. A process as in claim 1 wherein said phosphoric acid is added in an amount to provide from about 1.1 to about 1.7 equivalents per equivalent of said ferrous salt.

5. A process as in claim 1 wherein said heating is carried out at a temperature of about C. for a period of about one hour.

6. A process for the preparation of white iron phosphate of the formula FePO -2H O which comprises commingling in water ferrous sulfate, phosphoric acid in an amount to provide about 1.5 equivalents per equivalent of ferrous sulfate and sodium chlorate in an amount to provide about 1 equivalent per equivalent of ferrous sul- Pigme ntation Vehicle Top coat Percent blistering Percent rusting Bust creepage (in) Control Long oil alkyd Control FQPOLZIHO- trol Minimum Rust Creepage from score permitted=%".

Thus, the above results indicate the superior resistance fate, heating for about V2 hour at a temperature of about C., adjusting the pH to a value of about 2 to about 6,

to corrosion offered by iron phosphate when compared 45 and recovering white, insoluble iron phosphate which to an iron oxide barium sulfate control. precipitates.

WATER IMMERSION STUDY 7 Pigmentation Vehicle Top coat Duration Percent Percent rs.) blistering rusting FBPO42H2O Long oil alkyd None 256 None None. FeP04.2H-20 "do Black auto enamel 2, 256 0 Do. F0PO4.2H20.- Epoxy ester..- None 256 .do D0. FBPO42H5O .do Black auto enamol 2 256 o Do.

HUMIDITY STUDY Pigrncntation Vehicle Top coat Duration Percent Percent (hrs) blistering rusting FePO4 2Hz0- None 2, 256 Black auto enamelv 2, 256

None 25G FGPO-i-ZIHO o Black auto euamel 2, 256 do. Do.

References Cited UNITED STATES PATENTS 1,812,761 6/1931 Stevens et al. 23-105 2,227,928 1/ 1941 Drucker 106304 3,070,423 12/ 1962 Alexander 23-105 OTHER REFERENCES Van Wazer: vol. 1, Phosphorus and Its Compounds,

Interscience, 1958, p. 480.

OSCAR R. VERTIZ, Primary Examiner.

L. A. MARSH, Assistant Examiner. 

